Tris(2-chloroisopropyl) phosphate (TCPP), a widely used organophosphate flame retardant, has been recognized as an important atmospheric pollutant. It is notable that TCPP has potential for long-range atmospheric transport. However, its atmospheric fate is unknown, restricting its environmental risk assessment. Herein we performed quantum chemical calculations to investigate the atmospheric transformation mechanisms and kinetics of TCPP initiated by ·OH in the presence of O/NO/NO, and the effects of ubiquitous water on these reactions. Results show the H-abstraction pathways are the most favorable for the titled reaction. The calculated gaseous rate constant and lifetime at 298 K are 1.7 × 10 cmmolecule s and 1.7 h, respectively. However, when considering atmospheric water, the corresponding lifetime is about 0.5-20.2 days. This study reveals for the first time that water has a negative role in the ·OH-initiated degradation of TCPP by modifying the stabilities of prereactive complexes and transition states via forming hydrogen bonds, which unveils one underlying mechanism for the observed persistence of TCPP in the atmosphere. Water also influences secondary reaction pathways of selected TCPP radicals formed from the primary H-abstraction. These results demonstrate the importance of water in the evaluation of the atmospheric fate of newly synthesized chemicals and emerging pollutants.
Perfluorocarboxylic
acids (PFCAs) exhibit strong persistence in
sunlit surface waters and in radical-based treatment processes, where
superoxide radical (O2
•–) is an important and abundant reactive oxygen
species. Given that the role of O2
•– during the transformation of
PFCAs remains largely unknown, we investigated the kinetics and mechanisms
of O2
•–-mediated PFCAs attenuation through complementary experimental and
theoretical approaches. The aqueous-phase rate constants between O2
•– and C3–C8 PFCAs were measured using a newly designed in situ spectroscopic system. Mechanistically, bimolecular
nucleophilic substitution (SN2) is most likely to be thermodynamically
feasible, as indicated by density functional theory calculations at
the CBS-QB3 level of theory. This pathway was then investigated by ab initio molecular dynamics simulation with free-energy
samplings. As O2
•– approaches PFCA, the C–F bond at the alpha carbon is spontaneously
stretched, leading to the bond cleavage. The solvation mechanism for
O2
•–-mediated PFCA degradation was also elucidated. Our results indicated
that although the less polar solvent enhanced the nucleophilicity
of O2
•–, it also decreased the desolvation process of PFCAs, resulting in
reduced kinetics. With these quantitative and mechanistic results,
we achieved a defined picture of the O2
•–-initiated abatement of
PFCAs in natural and engineered waters.
The atmospheric chemistry of isoprene has broad implications for regional air quality and the global climate. Allylic radicals, taking 13−17% yield in the isoprene oxidation by • Cl, can contribute as much as 3.6−4.9% to all possible formed intermediates in local regions at daytime. Considering the large quantity of isoprene emission, the chemistry of the allylic radicals is therefore highly desirable. Here, we investigated the atmospheric oxidation mechanism of the allylic radicals using quantum chemical calculations and kinetics modeling. The results indicate that the allylic radicals can barrierlessly combine with O 2 to form peroxy radicals (RO 2• ). Under ≤100 ppt NO and ≤50 ppt HO 2• conditions, the formed RO 2 • mainly undergo two times "successive cyclization and O 2 addition" to finally form the product fragments 2-alkoxy-acetaldehyde (C 2 H 3 O 2• ) and 3-hydroperoxy-2-oxopropanal (C 3 H 4 O 4 ). The presented reaction illustrates a novel successive cyclization-driven autoxidation mechanism. The formed 3-hydroperoxy-2-oxopropanal product is a new isomer of the atmospheric C 3 H 4 O 4 family and a potential aqueous-phase secondary organic aerosol precursor. Under >100 ppt NO condition, NO can mediate the cyclization-driven autoxidation process to form C 5 H 7 NO 3 , C 5 H 7 NO 7 , and alkoxy radical-related products. The proposed novel autoxidation mechanism advances our current understanding of the atmospheric chemistry of both isoprene and RO 2• .
It
has been revealed that iodine species play important roles in
atmospheric new particle formations (NPFs) in pristine coastal areas.
However, it is unclear whether other atmospheric species, such as
NH3, for which the levels in coastal areas of China are
>2.5 × 1010 molecules·cm–3 are
involved in the NPFs of iodine species, although NH3 has
been proved to promote particle formation of H2SO4. Via high-level quantum chemical calculations and atmospheric cluster
dynamic code simulations, this study unveiled new mechanisms of nucleation,
in which NH3 mediates the formation of iodine particles
by assisting hydrolysis of I2O5 or reacting
with HIO3. The simulated formation rates of iodine–ammonia
clusters via the new mechanisms are much higher than those simulated
via sequential addition of HIO3 with subsequent release
of H2O, under the condition that NH3 concentrations
are higher than 1010 molecules·cm–3. The new mechanisms can well explain the observed cluster formation
rates at a coastal site in Zhejiang of China. The findings not only
expand the current understandings of the role of NH3 in
NPFs but also highlight the importance of monitoring and evaluating
NPFs via the iodine–ammonia cluster pathway in the coastal
areas of China and other regions worldwide.
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